In many surgical or diagnostic procedures it is necessary that a tubular medical instrument be placed within a body cavity. This instrument accomplishes a variety of purposes including the injection of fluids into the body or the withdrawal of fluids therefrom. Common examples of these types of instruments are catheters and infusion cannula tubes.
Catheter tubes in operation are inserted in the tortuous conduits of the body vessels (e.g., blood vessels) for several deca centimeters. The catheter tubing, therefore, is required to have the appropriate degree of stiffness to insure a smooth insertion combined with the necessary flexibility to allow its advance along the tortuous vessels without impairing the walls. Other important requirements for catheter tubes include dimensional stability, chemical and biological inertness and surface smoothness. These requirements apply equally to blood vessel catheters, urethra catheters and infusion cannula tubes.
Conventional tubular medical instruments for these purposes are made of rather stiff plastics such as polyethylene or nylon. Conventional infusion cannula tubing is about 12 or 13 cm in length and has an outside diameter (O.D.) of about 1.5 mm with an inside diameter (I.D.) of about 0.8 mm. These tubes are fitted at one end with an adapter through which a liquid medicine may be injected into, or a liquid extracted from, the body cavity via the tube. A metal piercing needle is inserted through the tube, the sharp tip of the needle projecting beyond the tube. This needle with the tubing thereon is then thrust through the skin into a blood vessel and both pushed forward until they reach the appropriate position. The needle is then withdrawn, leaving the infusion cannula and attached adapter in position. The adapter is closed with a plug. When an injection of medicine into, or an extraction of blood from the patient is desired, the plug is removed and the adapter is connected to a syringe or suction device.
In order to prevent the infusion cannula tubing from slipping out, the exposed portion must be affixed to the patient by some attaching means, commonly sutures or adhesive tape. In this fixed state, the conventional infusion cannula tubing, being rather rigid, will cause pain and discomfort should the patient move the area of the body in which the tubing is lodged. This problem is particularly acute since the insertion is usually made in a leg, arm, or thigh, thus, greatly restricting the movement of that limb.